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| Elasticity and Deforming Forces |
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| External forces acting on a body, bring about a change in its state or configuration. The latter is possible when the body is not free to move, but the molecules are compelled to change their positions. Such forces are called deforming forces. These forces bring about a change in the length, volume or shape. What happens to the body when these forces are removed? Obviously one expects the body to regain its shape. How does one account for this? |
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| On applying the forces, the interatomic distance becomes more than ro, thus increasing their potential energy (leading to instability). On removing the forces, the system tends to regain a minimum P.E. and as a result, attractive forces develop, restoring them to their original shape. The same applies when a body is subjected to a compressional force, where repulsive forces develop and restore the system to equilibrium. |
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| The property of the material of a body by virtue of which, the body regains its original length, volume and shape after the deforming forces have been removed, is called elasticity. |
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| Do all bodies possess this property of elasticity to the same extent? Substances like putty (clay), kneaded flour and paraffin wax undergo a permanent deformation. This property where bodies do not show a tendency to recover their original form after deforming forces are removed, is called plasticity. |
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